1. Field of the Invention
The present invention relates to an imaging sensor system which is to be installed on a movable object, such as a vehicle, that travels on a road, and which captures a road surface in its field of view, in particular, relates to a frontal view imaging and control device installed on a movable object which has function to automatically estimate the attitude of the imaging system with respect to the road surface on which the movable object travels.
2. Description of Related Art
An on-board frontal view imaging device is installed on the front portion of a vehicle in order to measure the position of a traveling subject vehicle so as to enable a stabilizing control or the like of the vehicle body.
Because such an on-board frontal view imaging device observes an exterior environment including a road surface while being installed on the vehicle, the attitude of a camera (an imaging unit) with respect to the vehicle and the road surface deviates from a standard attitude that has been determined during designing due to an installation error or load distribution.
Therefore, in order to compensate for shifting of the attitude of the imaging device from that at the installation thereof while using the images taken by such a camera, it is necessary to correct shifting of the attitude of the imaging device so that an apparatus, which caries out vehicle lane recognition and/or obstacle detection by using the images taken by the imaging device, exhibits designed performance by carrying out vehicle lane recognition (recognition of white lines or the like dram on the road surface) and/or vanishing point recognition thereby estimating the attitude of the imaging device.
In a conventional technology, when a vehicle travels straight at the center of a straight vehicle lane, the parameters representing the attitude of an imaging device are corrected based on the lane boundary lines drawn on the road surface and the vanishing point thereof and shifting of the attitude of the imaging device, i.e., shifting of the optical axis, is adjusted by image processing (see, for example, Japanese Unexamined Patent Application, First Publication No. 2002-259995, hereinafter referred to as Patent Document 1).
Moreover, in another conventional technology, the most frequent value (i.e., the mode) is selected from a histogram representing the measured parameter distribution, the mode is treated as an estimated value, and the optical axis is corrected by image processing (see, for example, Japanese Unexamined Patent Application, First Publication No. H11-337310, hereinafter referred to as Patent Document 2).
In another conventional technology, a vehicle lane and a vanishing point are determined by detecting peaks originating from a white line representing the boundary between vehicle lanes that is obtained from projection of a brightness image obtained by polar coordinate conversion with a vanishing point candidate as the origin (see, for example, Japanese Unexamined Patent Application, First Publication No. 2002-150302, hereinafter referred to as Patent Document 3).